1. Field of the Invention
The present invention is directed to a non-pneumatic tire (NPT) or combination of a tire and hub that supports an applied load by working in tension and is capable of serving as a replacement for pneumatic tires and an improvement over other forms of non-pneumatic tires.
2. Description of the Related Art
Non-pneumatic, or airless, tires have historically been comprised largely of an entirely solid substance. These solid tires made the ride rather uncomfortable for passengers and caused greater damage to the suspension of a vehicle, which had to compensate for their lack of “give.” Eventually, it was found that putting pressurized air in tires created a more comfortable ride. However, along with their advantages, pneumatic tires still possess some drawbacks.
The material that encloses standard pneumatic tires is susceptible to leaking the pressurized air it tries to withhold. This occurs both via leakage around the wheel rim, and on a smaller scale, when the rubber of the tire absorbs the oxygen. As a result, loss of pressure causes the tire to flatten in the area where the load is applied, subjecting a larger portion of the tire to the load with every revolution, leading to quicker degradation of the tire. Furthermore, a tire reliant upon pressurized air is susceptible to being punctured leading to rapid release of the pressurized air.
Focusing on fuel efficiency, safety and ride comfort, several attempts have been made to address the problems associated with pneumatic tires while retaining their advantages over solid non-pneumatic tires. By way of example, U.S. Published Application 2006/0113016 by Cron, et al, and assigned to Michelin, discloses a non-pneumatic tire that it commercially refers to as the Tweel™. In the Tweel™, the tire combines with the wheel. It is made up of four parts that are eventually bonded together: the hub, a spoke section, a reinforced annular band that surrounds the spoke section, and a rubber tread portion that contacts the ground.
Other alternatives to standard non-pneumatic tires have been attempted, including making solid tires out of polyurethane instead of rubber and suspending reinforcement materials within the polyurethane during molding. Another alternative is to use internal ribs made of a thermoplastic that are subsequently reinforced with glass fibers. A third alternative is to use an electroactive polymer that is capable of changing shape when an electrical current is applied. This allows the tire to change shape or size based upon road conditions by using the automobile's electrical system.